get-poetry: disallow installation of >= 1.2.0a1

Relates-to: #4040

get-poetry.py

@@ -449,6 +449,33 @@ class Installer:
 
                 break
 
+        def _is_supported(x):
+            mx = self.VERSION_REGEX.match(x)
+            vx = tuple(int(p) for p in mx.groups()[:3]) + (mx.group(5),)
+            return vx < (1, 2, 0)
+
+        if not _is_supported(version):
+            print(
+                colorize(
+                    "error",
+                    f"Version {version} does not support this installation method. Please specify a version prior to "
+                    f"1.2.0a1 explicitly using the '--version' option.\n"
+                    "Please see "
+                    "https://python-poetry.org/blog/announcing-poetry-1-2-0a1.html#deprecation-of-the-get-poetry-py-script "
+                    "for more information.",
+                )
+            )
+            return None, None
+
+        print(
+            colorize(
+                "warning",
+                "This installer is deprecated. "
+                "Poetry versions installed using this script will not be able to use 'self update' command to upgrade to "
+                "1.2.0a1 or later.",
+            )
+        )
+
         current_version = None
         if os.path.exists(POETRY_LIB):
             with open(
@@ -824,7 +851,7 @@ class Installer:
             HWND_BROADCAST,
             WM_SETTINGCHANGE,
             0,
-            u"Environment",
+            "Environment",
             SMTO_ABORTIFHUNG,
             5000,
             ctypes.byref(result),